Memory device and method for forming the same

ABSTRACT

A method for fabricating a memory device includes providing an initial semiconductor structure, including a base substrate, a stack structure of interlayer dielectric layers and first sacrificial layers; a channel trench formed through the stack structure. The method includes removing a portion of each first sacrificial layer from the channel trench to form a trapping-layer trench; forming a second sacrificial layer in the trapping-layer trench; forming a charge trapping film to fill the trapping-layer trench; and removing a portion of the charge trapping film from the channel trench to form a charge trapping layer; forming a tunneling layer and a channel layer on the sidewalls of the channel trench; removing the first sacrificial layers and the second sacrificial layer; forming a blocking layer on the charge trapping layer; and forming gate structures, in contact with the tunneling layer, between adjacent interlayer dielectric layers.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of International Application No.PCT/CN2020/079441, filed on Mar. 16, 2020, the entire content of whichis incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to the field of semiconductorfabrication technology and, more particularly, relates to memory devicesand their fabrication methods.

BACKGROUND

The production process of semiconductor electronic has made greatprogress with the development of the planar flash memory. However, inrecent years, the continuous development of the planar flash memoryencountered a number of challenges, such as physical limits, existinglithography limits, storage electron density limits, etc. In thiscontext, in order to solve the difficulties encountered by the planarflash memory and pursue lower production cost per storage unit, variousthree-dimensional (3D) flash memory structures, including 3D not-or(NOR) and 3D not-and (NAND), have emerged.

In the 3D flash memory of the NOR type structure, the storage units arearranged in parallel between the bit line and the ground line, while inthe 3D flash memory of the NAND type structure, the storage units arearranged in series between the bit line and the ground line. An NANDflash memory with a tandem structure has a lower read speed, but has ahigher write speed and erase speed. Therefore, the NAND flash memory issuitable for storing data. In addition, the NAND flash memory alsodemonstrates many advantages, such as small unit size and large storagecapacity, for data storage.

A charge trapping 3D memory is a basic device that allows forthree-dimensional integration. A key structure in a charge trapping 3Dmemory device is a gate stack, and the gate stack usually has amulti-layer structure which includes a channel layer, a tunneling layer,a charge trapping layer, and a barrier layer. The film layers of thegate stack are sequentially disposed on the sidewall surface of thechannel. The gate stack is used to control the charge storage functionof the memory device, and the channel layer of the gate stack provides apath for charge carriers. Therefore, the resistance of the channel layerplays an important role in the reliability and low-temperaturecharacteristics of the memory device.

As the demand on high storage density increases, the number of stacklayers in a 3D memory device may also increase, and the channel lengthmay be extended. When the channel length increases, the overallresistance of the channel also increases, and thus the conductionperformance of the channel may be degraded and the low-temperaturemobility of the carriers may be reduced. As such, the low-temperatureprogramming performance and the trans-temperature performance may not bedesired. Moreover, because the overall impedance of the channel is high,when performing program/read operations at an array level, theprogramming background noise may be enhanced, which may further causethe distribution of the threshold voltage to be widened at the arraylevel, and the device reliable window to be reduced.

Currently, the method to improve the conduction performance of a longchannel is to adjust the thickness of the channel layer and alsoincrease the crystallinity and the grain size of the channel layer.Adjusting the thickness of the channel layer and improving thecrystallinity and the grain size may be able to further increase theconduction current of the channel and reduce the trapping effect atgrain boundaries or at the layer interfaces, and thus the conductionperformance of the channel may be improved. However, as the number ofthe stack layers increases, more stringent requirements on thefabrication process may be imposed in order to further improve thequality of channel.

The disclosed memory device and fabrication method thereof are directedto solve one or more problems set forth above and other problems in theart.

BRIEF SUMMARY OF THE DISCLOSURE

One aspect of the present disclosure provides a method for fabricating amemory device. The method includes providing an initial semiconductorstructure, including a base substrate, a stack structure formed on thebase substrate and including a plurality of interlayer dielectric layersand a plurality of first sacrificial layers that are alternatelyarranged; and a channel trench formed through the stack structure andover the base substrate. The method also includes removing a portion ofeach first sacrificial layer close to the channel trench to form atrapping-layer trench recessed between adjacent interlayer dielectriclayers; forming a second sacrificial layer on a bottom and sidewalls ofthe trapping-layer trench and on sidewalls of the plurality ofinterlayer dielectric layers exposed in the channel trench; forming acharge trapping film to fill the trapping-layer trench; and removing aportion of each of the charge trapping film and the second sacrificiallayer from the channel trench. The remaining portion of the chargetrapping film forms a charge trapping layer. The method further includesforming a tunneling layer on the sidewalls of the charge trapping layerand a remaining second sacrificial layer along the channel trench andforming a channel layer on the tunneling layer; removing the pluralityof first sacrificial layers; removing the remaining second sacrificiallayer to expose portions of the tunneling layer between the chargetrapping layer and adjacent interlayer dielectric layers; forming ablocking layer on an exposed surface of the charge trapping layer; andforming a plurality of gate structures between adjacent interlayerdielectric layers. The plurality of gate structures is in contact withthe tunneling layer.

Another aspect of the present disclosure provides a memory device. Thememory device includes a base substrate; a plurality of interlayerdielectric layers and a plurality of gate structures that arealternately stacked to form a stacked structure over the base substrate;a tunneling layer formed along a sidewall of the stacked structure; achannel layer formed on the tunneling layer along the sidewall of thestacked structure, the tunneling layer separating the channel layer fromthe stacked structure; a charge trapping layer, formed between thetunneling layer and the plurality of gate structures in a directionperpendicular to the tunneling layer, and between adjacent interlayerdielectric layers; a blocking layer formed on the tunneling layer,enveloping the charge trapping layer, and between adjacent interlayerdielectric layers. The blocking layer separates the charge trappinglayer from the plurality of gate structures; a side surface of thecharge trapping layer is in contact with the tunneling layer; and aportion of each gate structure directly in contact with the tunnelinglayer separates the blocking layer from an adjacent interlayerdielectric layer.

Other aspects of the present disclosure can be understood by thoseskilled in the art in light of the description, the claims, and thedrawings of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are merely examples for illustrative purposesaccording to various disclosed embodiments and are not intended to limitthe scope of the present disclosure.

FIG. 1 illustrates a schematic cross-sectional view of a 3D NAND memorydevice;

FIG. 2 illustrates an enlarged schematic view of the structure shown ina dashed-line frame in FIG. 1;

FIG. 3 illustrates a flowchart of an exemplary fabrication methodaccording to various embodiments of the present disclosure;

FIGS. 4-15 illustrate schematic views of semiconductor structures atcertain stages of an exemplary method according to various embodimentsof the present disclosure; and

FIG. 16 illustrates an enlarged schematic view of the structure shown ina dashed-line frame in FIG. 14.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments of theinvention, which are illustrated in the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts.

FIG. 1 illustrates a schematic cross-sectional view of a 3D NAND memorydevice, and FIG. 2 illustrates an enlarged schematic view of thestructure shown in a dashed-line frame in FIG. 1. Referring to FIGS.1-2, a 3D NAND memory device includes a base substrate 100, and a stackstructure including a plurality of interlayer dielectric layers 101 anda plurality of gate layers 102. The plurality of interlayer dielectriclayers 101 and the plurality of gate layers 102 are alternately disposedto form the stack structure. The 3D memory device also includes aplurality of channel trenches 103 formed through the stack structure andover the base substrate 100, and an epitaxial layer 104 formed on thebottom of each channel trench 103 and over the base substrate 100.

The 3D NAND memory device further includes a blocking layer 111, acharge trapping layer 112, a tunneling layer 113, and a channel layer114 sequentially formed on the sidewall surface of the channel trench103. As such, the blocking layer 111, the charge trapping layer 112, thetunneling layer 113, and the channel layer 114 together form a gatestack on the sidewall surface of the channel trench 103.

It should be noted that FIGS. 1-2 only illustrate the structures thatare relevant to the present disclosure, the 3D NAND memory device mayfurther include other components and/or structures for achievingcomplete functions of the device.

In the 3D NAND memory device, the gate stack formed by the blockinglayer 111, the charge trapping layer 112, the tunneling layer 113, andthe channel layer 114 serves as a key structure of the charge trapping3D memory. In the multi-layer gate stack, the tunneling layer 113 ismade of silicon oxide, the charge trapping layer 112 is made of siliconnitride, and the barrier layer 111 is made of silicon oxide. The gatestack is used to control the charge storage function of the memory, andthe channel layer 114 of the gate stack provides a path for chargecarriers. Therefore, the resistance of the channel layer plays animportant role in the reliability and low-temperature characteristics ofthe memory device.

To improve the storage density, in the 3D NAND memory device, the numberof the stack layers is large and the channel length is long. Therefore,the overall resistance of the channel increases, causing the conductionperformance of the channel to be degraded and the mobility of thecarriers to be reduced at low temperatures. As such, the low-temperatureprogramming performance and the trans-temperature performance may not bedesired. Moreover, because the overall impedance of the channel is high,when performing program/read operations at an array level, theprogramming background noise may be enhanced, which may further causethe distribution of the threshold voltage to be widened at the arraylevel, and the device reliable window to be reduced.

According to existing technology, in order to improve the conductionperformance of a long channel, the thickness of the channel layer may beadjusted, and the crystallinity and the grain size of the channel layermay be increased. However, as the number of the stack layers increases,more stringent requirements on the fabrication process may be imposed inorder to further improve the quality of channel.

The present disclosure provides a method for fabricating a 3D NANDmemory device. FIG. 3 illustrates a flowchart of an exemplaryfabrication method according to various embodiments of the presentdisclosure, and FIGS. 4-16 illustrate schematic views of semiconductorstructures at certain stages of an exemplary method according to variousembodiments of the present disclosure.

Referring to FIG. 3, an initial semiconductor structure may be provided,and the initial semiconductor structure may include a base substrate; astack structure including a plurality of interlayer dielectric layersand a plurality of first sacrificial layers that are alternatelydisposed on the base substrate; a channel trench formed through thestack structure and over the base substrate; and an epitaxial layerformed on the bottom of the channel trench and over the base substrate(S401). FIG. 4 illustrates a schematic cross-sectional view of asemiconductor structure consistent with various embodiments of thepresent disclosure, and FIG. 5 illustrates an enlarged schematic view ofthe structure shown in a dashed-line frame in FIG. 4.

Referring to FIGS. 4-5, an initial semiconductor structure may beprovided. The initial semiconductor structure may include a basesubstrate 200, a stack structure including a plurality of interlayerdielectric layers 201 and a plurality of first sacrificial layers 221that are alternately disposed on the base substrate 200; a channeltrench 203 formed through the stack structure and over the basesubstrate 200; and an epitaxial layer 204 formed on the bottom of thechannel trench 203 and over the base substrate 200.

In one embodiment, the base substrate 200 may be made of silicon,germanium, silicon germanium, or any appropriate semiconductor material,the plurality of interlayer dielectric layers 201 may be made of anoxide, e.g. silicon oxide, and the plurality of first sacrificial layers221 may be made of a nitride, e.g. silicon nitride. In one embodiment,the thickness of each first sacrificial layer 221 may be in a range ofapproximately 20 nm to 40 nm.

Further, returning to FIG. 3, a portion of each first sacrificial layerclose to the channel trench may be removed to form a trapping-layertrench recessed between adjacent interlayer dielectric layers (S402).FIG. 6 illustrates a schematic cross-sectional view of a semiconductorstructure consistent with various embodiments of the present disclosure.

Referring to FIG. 6, a portion of each first sacrificial layer 221 thatis close to the channel trench 203 (referring to FIG. 4) may be removedto form a trapping-layer trench 210 recessed between adjacent interlayerdielectric layers 201. In one embodiment, the portion of the firstsacrificial layer 221 may be removed through a wet etching process.After removing the portion of the first sacrificial layer 221, the depthof the trapping-layer trench 210 in a direction perpendicular to thesidewall surface of the channel trench 203 may be in a range ofapproximately 20 nm to 50 nm. It should be noted that during the etchingprocess, the etching rate of the material used for forming the firstsacrificial layer 221 may be substantially larger than the etching rateof the material used for forming the interlayer dielectric layer 201,and thus the plurality of interlayer dielectric layers 201 may beslightly removed or may even remain unchanged after the etching process.

Further, returning to FIG. 3, a second sacrificial layer may be formedon the bottom and sidewalls of the trapping-layer trench and thesidewalls of the plurality of interlayer dielectric layers exposed inthe channel trench (S403). FIG. 7 illustrates a schematiccross-sectional view of a semiconductor structure consistent withvarious embodiments of the present disclosure.

Referring to FIG. 7, a second sacrificial layer 222 may be formed on thebottom and sidewalls of the trapping-layer trench 210 and on thesidewalls of the plurality of interlayer dielectric layers 201 exposedin the channel trench 203 (referring to FIG. 4). The second sacrificiallayer 222 may also cover the sidewall surface of the channel trench 203(referring to FIG. 4). Because the depth direction of the trapping-layertrench 210 is perpendicular to the sidewall surface of the channeltrench 203, the sidewall surface of the trapping-layer trench 210 mayexpose adjacent interlayer dielectric layers 201, and the bottom surfaceof the trapping-layer trench 210 may expose the corresponding firstsacrificial layer 221.

In one embodiment, the second sacrificial layer 222 may be made of GeO₂,polycrystalline silicon, a high-k dielectric material (e.g., a materialwith a relative dielectric constant larger than 3.9), etc. The secondsacrificial layer 222 may be formed through a chemical vapor deposition(CVD) process, an atomic layer deposition (ALD) process, or any otherappropriate deposition process. The thickness of the second sacrificiallayer may be in a range of approximately 3 nm to 5 nm.

Further, returning to FIG. 3, a charge trapping film may be formed tofill the trapping-layer trench and also cover the sidewall surface ofthe channel trench (S404). FIG. 8 illustrates a schematiccross-sectional view of a semiconductor structure consistent withvarious embodiments of the present disclosure.

Referring to FIG. 8, a charge trapping film 232 may be formed to fillthe trapping-layer trench 210 (referring to FIG. 6). The charge trappingfilm 232 may also cover the sidewall surface of the channel trench 203(referring to FIG. 4). In one embodiment, the charge trapping film 232may be made of silicon nitride, silicon oxynitride, or any otherappropriate material. Alternatively, in other embodiments, the chargetrapping film may have a composite structure formed by silicon nitrideand silicon oxynitride. In one embodiment, the charge trapping film 232may be formed through a CVD process, an ALD process, or any otherappropriate deposition process.

In one embodiment, during a subsequently performed acid etching process,the etch rate of the material used for forming the second sacrificiallayer 222 may be substantially larger than the etch rate of the materialused for forming the charge trapping film 232.

Further, returning to FIG. 3, a portion of each of the charge trappingfilm and the second sacrificial layer may be removed from the channeltrench, such that the remaining portion of the charge trapping film mayform a charge trapping layer (S405). FIG. 9 illustrates a schematiccross-sectional view of a semiconductor structure consistent withvarious embodiments of the present disclosure.

Referring to FIG. 9, a portion of the charge trapping film 232(referring to FIG. 8) and a portion of the second sacrificial layer 222may be removed from the channel trench 203 (referring to FIG. 4) untilthe sidewall surfaces of the plurality of interlayer dielectric layers201 are exposed in the channel trench 203. The remaining portion of thecharge trapping layer 232 may form a charge trapping layer 212. As such,in a direction perpendicular to the sidewall surface of the channeltrench 203, the sidewall surfaces of the charge trapping layer 212 andthe second sacrificial layer 222 may be leveled with the sidewallsurfaces of the plurality of interlayer dielectric layers 201. Inaddition, the charge trapping layer 212 may include a plurality ofdiscrete portions with each portion located between two adjacentinterlayer dielectric layers 201 and separated from the interlayerdielectric layers 201 by the second sacrificial layer 222. In oneembodiment, the process of removing the portion of the charge trappingfilm 232 and the second sacrificial layer 222 formed on the sidewallsurface of the channel trench 203 may be a dry etching process or a wetetching process.

Further, returning to FIG. 3, a tunneling layer may be formed on thesidewalls of the charge trapping layer and the remaining secondsacrificial layer along the channel trench and a channel layer may beformed on the tunneling layer (S406). FIG. 10 illustrates a schematiccross-sectional view of a semiconductor structure consistent withvarious embodiments of the present disclosure.

Referring to FIG. 10, a tunneling layer 213 may be formed on thesidewalls of the charge trapping layer 212 and the remaining secondsacrificial layer 222 along the channel trench 203 (referring to FIG.4). Moreover, a channel layer 214 may be formed on the tunneling layer213. In one embodiment, the tunneling layer 213 may be made of siliconoxide, silicon oxynitride, or a high-k dielectric material. In otherembodiments, the tunneling layer 213 may have a composite structureformed by silicon oxide, silicon oxynitride, and high-k dielectricmaterials. In one embodiment, the tunneling layer 213 may be formedthrough a CVD process, an ALD process, or any other appropriatedeposition process. In one embodiment, the thickness of the tunnelinglayer 213 may be in a range of approximately 1 nm to 10 nm.

In one embodiment, the channel layer 214 may be made of amorphoussilicon, polycrystalline silicon, or any other appropriate material, andthe channel layer 214 may be connected to the epitaxial layer 204 formedat the bottom of the channel trench 203 (referring to FIG. 4). In oneembodiment, the channel layer 214 may be formed through a CVD process,an ALD process, or any other appropriate deposition process.

Further, returning to FIG. 3, the plurality of first sacrificial layersmay be removed (S407). FIG. 11 illustrates a schematic cross-sectionalview of a semiconductor structure consistent with various embodiments ofthe present disclosure.

Referring to FIG. 11, the plurality of first sacrificial layers 221(referring to FIG. 10) may be removed. The plurality of firstsacrificial layers 221 may be removed through an acid etching process.In one embodiment, prior to removing the plurality of first sacrificiallayers 221, a plurality of common-source trenches (not shown) may beformed in the stack structure. In one embodiment, a channel trenchprocess, may be completed before forming the plurality of common-sourcetrenches. For example, a contact plug for the channel layer may beformed in the channel trench. The plurality of common-source trenchesmay be formed in the stack structure through an etching process.Further, by performing an acid etching process through the plurality ofcommon-source trenches, the plurality of first sacrificial layers in thestack structure may be removed.

Returning to FIG. 3, the remaining second sacrificial layer may beremoved to expose portions of the tunneling layer between the chargetrapping layer and the adjacent interlayer dielectric layers (S408).FIG. 12 illustrates a schematic cross-sectional view of a semiconductorstructure consistent with various embodiments of the present disclosure.

Referring to FIG. 12, the remaining second sacrificial layer 222(referring to FIG. 11) may be further removed, such that portions of thetunneling layer 213 may be exposed between the charge trapping layer 212and the adjacent interlayer dielectric layers 201. In one embodiment,after removing the plurality of first sacrificial layers 221 (referringto FIG. 10), the etching process may further remove the secondsacrificial layer 222.

In one embodiment, the second sacrificial layer 222 may be completelyremoved. In other embodiment, the second sacrificial layer 222 may besubstantially removed, and only a small portion of the secondsacrificial layer 222 may remain at a position close to the tunnelinglayer 213.

Further, returning to FIG. 3, a blocking layer may be formed on theexposed surface of the charge trapping layer (S409). FIG. 13 illustratesa schematic cross-sectional view of a semiconductor structure consistentwith various embodiments of the present disclosure.

Referring to FIG. 13, a blocking layer 211 may be formed on the exposedsurface of the charge trapping layer 212. In one embodiment, theblocking layer 211 may be made of silicon oxide, and the thickness ofthe blocking layer 211 may be in a range of approximately 2 nm to 10 nm.The blocking layer 211 may be formed through a thermal oxidizationprocess or an in-situ steam generation (ISSG) process, and thus theblocking layer 211 may be a dense film layer made of silicon oxide. Inone embodiment, after forming the blocking layer 211 on the exposedsurface of the charge trapping layer 212, the blocking layer 211 may bespaced from each adjacent interlayer dielectric layer 201 by a gap witha size in a range of approximately 3 nm to 5 nm in a direction parallelto the sidewall surface of the channel trench.

Further, returning to FIG. 3, a plurality of gate structures may beformed to fill the empty space between adjacent interlayer dielectriclayers (S410). FIG. 14 illustrates a schematic cross-sectional view of asemiconductor structure consistent with various embodiments of thepresent disclosure, and FIG. 15 illustrates a schematic cross-sectionalview of another semiconductor structure consistent with variousembodiments of the present disclosure. FIG. 16 illustrates an enlargedschematic view of the structure shown in a dashed-line frame in FIG. 14.

Referring to FIGS. 14-15, a plurality of gate structures 202 may beformed to fill the empty space between adjacent interlayer dielectriclayers 201. Referring to FIG. 16, in one embodiment, each gate structure202 may be a metal gate structure, including a high-k dielectric layer241, a work function layer 242, and a metal-gate layer 243 sequentiallyformed in the empty space between the corresponding interlayerdielectric layers 201. For example, the high-k dielectric layer 241 maybe formed on the exposed surfaces of the plurality of interlayerdielectric layers 201, the tunneling layer 213, and the blocking layer211. The work function layer 142 may then be formed on the exposedsurface of the high-k dielectric layer 241 between adjacent interlayerdielectric layers 201. Further, the metal-gate layer 243 may be formedon the interlayer dielectric layers 201.

In one embodiment, referring to FIG. 14, the space between the blockinglayer 211 and the plurality of interlayer dielectric layers 201 may befully filled by the plurality of gate structures 202. In otherembodiments, referring to FIG. 15, when forming the gate structure 202,the metal-gate layer 243 (referring to FIG. 16) may not be completelyfilled into the space between the blocking layer 211 and the pluralityof interlayer dielectric layers 201, leaving a plurality of voidsbetween the blocking layer 211 and the plurality of interlayerdielectric layers 201.

Referring to FIG. 14, as indicated by a circle, the gate structure 202may be directly in contact with the tunneling layer 213 at positionsclose to each corner formed by the tunneling layer 213 and the pluralityof interlayer dielectric layers 201. Therefore, along a Y direction,e.g. the direction parallel to the sidewall surface of the channeltrench 203 (referring to FIG. 4), the distance between the channel layer214 and the gate structure 202 may vary, and at the positions where thegate structure 202 is directly in contact with the tunneling layer 213,the distance between the channel layer 214 and the gate structure 202may be the shortest. Correspondingly, when performing program/readoperations, the resistance of the channel at these positions may be low.As such, the overall resistance of the channel may be reduced, theconduction current through the channel layer 214 may be effectivelyincreased, and thus the response speed to program/read operations may beimproved. Moreover, as the overall resistance of the channel decreases,the programming background noise also decreases, and thus thearray-level widening effect of the distribution of the threshold voltagemay be suppressed.

According to the disclosed method for fabricating a 3D NAND memorydevice, a portion of the gate structure is directly in contact with thetunneling layer. Therefore, at the positions where the gate structure isdirectly in contact with the tunneling layer, the distance from the gateto the channel is reduced, and correspondingly, when performingprogram/read operations, the resistance of the channel at thesepositions may be low. As such, the overall resistance of the channel maybe reduced, the conduction current through the channel may beeffectively increased, and thus the response speed to program/readoperations may be improved. In addition, the disclosed method alsoimproves the channel conduction performance at low temperatures, therebyimproving the low-temperature programming performance and thetrans-temperature performance. Moreover, as the overall resistance ofthe channel decreases, the programming background noise also decreases,and thus the array-level widening effect of the distribution of thethreshold voltage may be suppressed.

The present disclosure also provides a memory device. FIG. 14illustrates a schematic cross-sectional view of an exemplary memorydevice consistent with various embodiments of the present disclosure.FIG. 16 illustrates an enlarged schematic view of the structure shown ina dashed-line frame in FIG. 14.

Referring to FIG. 14, the memory device may include a base substrate(not shown), and a plurality of interlayer dielectric layers 201 and aplurality of gate structures 202 that are alternately stacked over thebase substrate to form a stack structure. In one embodiment, thedistance between adjacent interlayer dielectric layers 201 may be in arange of approximately 20 nm to 40 nm.

The memory device may include a tunneling layer 213 formed along thesidewall of the stacked structure. The memory device may further includea channel layer 214 formed on the tunneling layer 213 opposite to theplurality of interlayer dielectric layers 201 and the plurality of gatestructures 202. The tunneling layer 213 may separate the channel layer214 from the plurality of interlayer dielectric layers 201 and theplurality of gate structures 202.

In one embodiment, the tunneling layer 213 may be made of silicon oxide,silicon oxynitride, or a high-k dielectric material. In otherembodiments, the tunneling layer 213 may have a composite structureformed by silicon oxide, silicon oxynitride, and high-k dielectricmaterials. In one embodiment, the thickness of the tunneling layer 213may be in a range of approximately 1 nm to 10 nm. In one embodiment, thechannel layer 214 may be made of amorphous silicon, polycrystallinesilicon, or any other appropriate material.

The memory device may also include a charge trapping layer 212 formedbetween the tunneling layer 213 and the plurality of gate structures 202in the direction perpendicular to the tunneling layer 213, and betweenadjacent interlayer dielectric layers 201. A side surface of the chargetrapping layer 212 may be directly in contact with the tunneling layer213, and a portion of each gate structure of the plurality of gatestructures 202 directly in contact with the tunneling layer 213 mayseparate the charge trapping layer 212 from the plurality of interlayerdielectric layers 201. In one embodiment, the dimension of the chargetrapping layer 212 in the direction perpendicular to the tunneling layer213 may be in a range of approximately 18 nm to 40 nm.

The memory device may further include a blocking layer 211 formed on thecharge trapping layer 212. The blocking layer 211 may separate thecharge trapping layer 212 from the gate structure 202. Therefore, theblocking layer 211 and a portion of each gate structure 202 may bedirectly in contact with the tunneling layer 213 and thus separate thecharge trapping layer 212 from the plurality of interlayer dielectriclayers 201. In one embodiment, the thickness of the blocking layer 211may be in a range of approximately 2 nm to 10 nm. In one embodiment, ina direction perpendicular to the plurality of interlayer dielectriclayers 201, the thickness of the portion of the gate structure 202 thatseparates the blocking layer 211 from an adjacent interlayer dielectriclayer 201 may be in a range of approximately 3 nm to 5 nm.

In one embodiment, referring to FIG. 14, the space between the blockinglayer 211 and the plurality of interlayer dielectric layers 201 may befully filled by the plurality of gate structures 202. In otherembodiments, referring to FIG. 15, the space between the blocking layer211 and the plurality of interlayer dielectric layers 201 may not befully filled by the plurality of gate structures 202.

In one embodiment, referring to FIG. 16, each gate structure 202 mayinclude a high-k dielectric layer 241 formed on the interlayerdielectric layer 201. The high-k dielectric layer 241 may also be formedon the tunneling layer 213 and the blocking layer 211. The gatestructure 202 may also include a work function layer 242 formed on thehigh-k dielectric layer 241, and a metal-gate layer 243 formed on thework function layer 242.

According to the disclosed memory device, a portion of the gatestructure is directly in contact with the tunneling layer. Therefore, atthe positions where the gate structure is directly in contact with thetunneling layer, the distance from the gate to the channel is reduced,and correspondingly, when performing program/read operations, theresistance of the channel at these positions may be low. As such, theoverall resistance of the channel may be reduced, the conduction currentthrough the channel may be effectively increased, and thus the responsespeed to program/read operations may be improved. In addition, thedisclosed memory device also improves the channel conduction performanceat low temperatures, thereby improving the low-temperature programmingperformance and the trans-temperature performance. Moreover, as theoverall resistance of the channel decreases, the programming backgroundnoise also decreases, and thus the array-level widening effect of thedistribution of the threshold voltage may be suppressed.

The above detailed descriptions only illustrate certain exemplaryembodiments of the present invention, and are not intended to limit thescope of the present invention. Those skilled in the art can understandthe specification as whole and technical features in the variousembodiments can be combined into other embodiments understandable tothose persons of ordinary skill in the art. Any equivalent ormodification thereof, without departing from the spirit and principle ofthe present invention, falls within the true scope of the presentinvention.

What is claimed is:
 1. A method for fabricating a memory device,comprising: providing an initial semiconductor structure, including abase substrate, a stack structure formed on the base substrate andincluding a plurality of interlayer dielectric layers and a plurality offirst sacrificial layers that are alternately arranged; and a channeltrench formed through the stack structure and over the base substrate;removing a portion of each first sacrificial layer close to the channeltrench to form a trapping-layer trench recessed between adjacentinterlayer dielectric layers; forming a second sacrificial layer on abottom and sidewalls of the trapping-layer trench and on sidewalls ofthe plurality of interlayer dielectric layers exposed in the channeltrench; forming a charge trapping film to fill the trapping-layertrench; removing a portion of each of the charge trapping film and thesecond sacrificial layer from the channel trench, wherein a remainingportion of the charge trapping film forms a charge trapping layer;forming a tunneling layer on sidewalls of the charge trapping layer anda remaining second sacrificial layer along the channel trench andforming a channel layer on the tunneling layer; removing the pluralityof first sacrificial layers; removing the remaining second sacrificiallayer to expose portions of the tunneling layer between the chargetrapping layer and adjacent interlayer dielectric layers; forming ablocking layer on an exposed surface of the charge trapping layer; andforming a plurality of gate structures between adjacent interlayerdielectric layers, wherein the plurality of gate structures is incontact with the tunneling layer.
 2. The method according to claim 1,wherein: the plurality of interlayer dielectric layers is made ofsilicon oxide; and the plurality of first sacrificial layers is made ofsilicon nitride.
 3. The method according to claim 1, wherein: athickness of each first sacrificial layer of the plurality of firstsacrificial layers is in a range of approximately 20 nm to 40 nm.
 4. Themethod according to claim 1, wherein: a depth of the trapping-layertrench in a direction perpendicular to a sidewall of the channel trenchis in a range of approximately 20 nm to 50 nm.
 5. The method accordingto claim 1, wherein: the charge trapping film is made of a materialincluding at least one of silicon nitride, silicon oxynitride, or ahigh-k dielectric material.
 6. The method according to claim 1, wherein:the second sacrificial layer is made of GeO2, polycrystalline silicon,or a high-k dielectric material; and a thickness of the secondsacrificial layer is in a range of approximately 3 nm to 5 nm.
 7. Themethod according to claim 1, wherein: each gate structure of theplurality of gate structures includes a high-k dielectric layer, a workfunction layer, and a metal-gate layer sequentially formed betweencorresponding interlayer dielectric layers.
 8. The method according toclaim 1, wherein: the tunneling layer is made of a material including atleast one of silicon oxide, silicon oxynitride, or a high-k dielectricmaterial; and a thickness of the tunneling layer is in a range ofapproximately 1 nm to 10 nm.
 9. The method according to claim 1,wherein: a thickness of the blocking layer is in a range ofapproximately 2 nm to 10 nm.
 10. The method according to claim 9,wherein: the blocking layer is formed on the exposed surface of thecharge trapping layer through a thermal oxidization process or anin-situ steam generation (ISSG) process.
 11. The method according toclaim 1, further including: an epitaxial layer formed on a bottom of thechannel trench and over the base substrate.